The Isolation and Purification of Thyroid Peroxidase*

A procedure for the extraction and isolation of the peroxidase in pig thyroid glands has been described. The enzyme has been purified by gel filtration and diethylaminoethyl chromatography, and its spectral properties suggest that the enzyme is a typical hemoprotein peroxidase, while gel filtration experiments have shown it to have a molecular weight of 104,000. The specific activity of the preparation was significantly higher than that of other reported preparations. The purified peroxidase can oxidize 48.9 pmoles of guaiacol per mm per mg of protein, or 7.35 pmoles of iodide ion per min per mg of protein. The rate constant, kl, between the enzyme and hydrogen peroxide was found to be 1.1 x 10’ M” see-1 at pH 7.4. The rate constant, 4, between Complex II and the hydrogen donor had a value of 1.1 X lo5 M-’ set-1 for guaiacol at pH 7.4, and 1.3 X lo6 I@ set-l for KI at pH 7.0. The temperature optimum for the enzyme has been found at 3740“. The enzyme can iodinate tyrosine and thyroglobulin.